The present invention relates to reduction of electricity consumption of a matrix-type display apparatus.
Recently, there has been a rapid acceleration in application of liquid crystal display apparatuses in apparatuses, such as word processors, lap top-type personal computers, and pocket-sized televisions. Among the liquid crystal display apparatuses, especially, a reflection-type liquid crystal display apparatus (LCD) draws an attention. Because display of the reflection-type LCD is carried out by reflecting incident light from an outside, the reflection-type LCD requires no back light, thus contributing to low electricity consumption and thin thickness, which leads to a light weight of apparatuses using the LCD of the reflection type.
Conventional LCDs of the reflection type are broadly classified into (a) one using a segment display method, (b) one using a simple multiplex driving method, and (c) one using an active matrix driving method. By using the segment display method, it is possible to display only simple numbers or pictorial symbols, which are used in watches and the like. The simple multiplex driving method and the active matrix driving method, which uses an active element such as a Thin Film Transistor (TFT), can be used for complicated displays of personal computers, portable information terminals and the like. It is desired commonly for all the three methods to have a lower electricity consumption.
As a method of reducing the electricity consumption of the segment display method, Japanese Unexamined Patent Application, Tokukaihei, No. 5-232447 (published on Sep. 10, 1993) discloses that identical potential is applied into a common electrode and a segment electrode so as to acquire a stable display totally in white or black color during a standby time, that is, while no image is displayed and displayed is an all-while display or an all black-display. Moreover, Japanese Unexamined Patent Application, Tokukaihei, No. 2-210492 (published on Aug. 21, 1990) discloses a method for making a high impedance state in an MOS transistor, which directly drives a liquid crystal during the standby time, so that electricity consumption of a driving circuit is reduced. Because the prior arts are for the LCD using the segment display method, the prior arts are limited to display the simple numbers and pictorial symbols, and cannot be applied to those apparatuses such as the personal computers and the portable information terminals, which display complicated information.
Furthermore, it is difficult to employ those driving methods in a matrix-type liquid crystal display apparatus. Going into details, for example, a matrix-type LCD of 4xc3x974 size as shown in FIG. 15 have scanning signals as shown in FIG. 16. The scanning signals are respectively supplied to scanning signal lines G(0) to G(3), so that a selective voltage is applied in order into the scanning signals G(0) to G(3). In a synchronizing manner with the scanning signals of the thus selected respective scanning lines, data signals are supplied to data signal lines S(0) to S(3), so as to write in each pixel an electric charge, which is in accordance with a data. After scanning of a bottom line and a vertical blanking period of a short time, scanning is started again from a first line, as shown in FIG. 17. An original reason why the vertical blanking period is provided is to have a period during which an electron beam from an electron gun, which is provided inside a CRT, can return to its original position. Therefore, LCDs actually requires no vertical blanking period. However, in order to reproduce a general television image or the like on LCDs, the vertical blanking period is provided to LCDs so as to give a compatibility to LCDs with respect to television images according to NTSC (National Television System Committee) or the like.
As discussed above, in case of the matrix-type LCD, it is necessary to drive plural pixels on data signal lines aligned in a vertical direction on a screen. Thus, the matrix-type LCD has no such data signal output to drive single pixel alone, unlike a segment output of the segment display method. Therefore, although application of a driving method of the segment display method in the matrix-type LCD keeps the data signal lines and opposite electrode of the pixels at the high impedance state after electric charges are written in pixels on a bottom line on one picture (one picture in one frame), the pixels other than the pixels in a bottom line of the screen does not maintain an electric charge written therein, thereby failing to achieve a stable display on the matrix-type LCD.
Among such matrix-type LCDs, a matrix-type LCD using the simple multiplex driving method has a size of 2-inch and consumes electricity in a range of from 10 mW to 15 mW, which is sufficiently small. However, the matrix-type LCD of the simple multiplex driving method is disadvantaged in its low brightness and contrast and slow responding speed, which are fundamental display qualities. On the other hand, the matrix-type LCD employing the active driving method, in which the TFT or the like is used, is excellent in brightness and contrast, and has a fast responding speed, thereby being satisfactory in terms of the fundamental display qualities. However, even the matrix-type LCD of 2-inch size consumes electricity in a range of from 100 mW to 150 mW, which is unsatisfactorily high.
In view of the above problems, intensive research and developments have been carried out, aiming to attain sufficiently low electricity consumption and good display qualities. For example, Japanese Unexamined Utility Model Application, Jitsukaisho, No. 60-50573 (published on Apr. 9, 1985), and Japanese Unexamined Patent Application, Tokukaihei, No. 10-10489 (published on Jan. 16, 1998) disclose methods of achieving low electricity consumption. The methods in those publications, taking note of how television signals are transmitted, take advantage of the vertical blanking period, during which no data exists, so as to stop operation of a peripheral driving circuit during the vertical blanking period, thereby reducing the electricity consumption.
Moreover, another method is disclosed in Japanese Unexamined Patent Application, Tokukaihei, No. 9-107563 (published on Apr. 22, 1997), which relates to reduction of electricity consumption of a head mounting-type display apparatus for field sequential three-dimensional (3-D) image display, having two liquid crystal panels respectively for each eye. In this method, only one of the liquid crystal panels is driven during one field, while the other is stopped operating during the one field. In this way, the liquid crystal panels are driven in turn per field period.
As still another method, SIDxe2x80x2 95 symposium digest, pages 249 to 252 (Titled: Multi-Field Driving Method For Reducing LCD Power Consumption) and Japanese Unexamined Patent Application, Tokukaihei, NO. 3-271795 (published on Dec. 3, 1991) discuss a multi-field driving method, in which scanning of one picture is carried out in such a manner that every other scanning signal line or every other several scanning signal lines are scanned so that scanning is performed in installment (that is, not at once, but divided into a plurality of times). In one time (one of the divided plurality of times) of the scanning, a voltage in the data signal line is not inverted (changed) in terms of polarity, thereby reducing electricity consumption of a data signal line driver. Moreover, this method also aims to realize a display free from flickering as a whole, by cancelling out flickering on one line with flickering on a neighboring line thereof. The flickering is changes of brightness caused between each line, and flickering on each line has an opposite polarity with respect to flickering on neighboring lines thereof.
Furthermore, for example, Japanese Unexamined Patent Application, Tokukaihei, No. 6-342148 (published on Dec. 13, 1994) discloses a method in which a ferroelectric liquid crystal is used in a liquid crystal panel so that the liquid crystal panel will function as a memory, so as to reduce a driving frequency (refresh rate), whereby the electricity consumption is lowered.
However, with the method in which the peripheral driving circuit is stopped operating during the vertical blanking period, the electricity consumption is reduced by about 5% only, because the vertical blanking period shares only about 8% of a whole period, as also recited in the above-mentioned Japanese Unexamined Utility Model, Jitsukaisho, No 60-50573.
Moreover, regarding the method disclosed in the above-mentioned Japanese Unexamined Patent Application, Tokukaihei, No. 9-107563, at least one of the liquid crystal panels is driven throughout all the field periods. As a result, the electricity consumption may not be increased but cannot be reduced with this method. Furthermore, in this method, an image with little flickering is attained when the display apparatus is of a both-eyed head-mounting type because at least one of the liquid crystal panels is refreshed. However, generally speaking, LCDs can attain display free from flickering when the LCDs are driven at not less than 30 Hz or especially 45 Hz or more. Therefore, application of this method in a liquid crystal panel to be viewed directly, the flickering becomes more perceptible.
Moreover, even if the multi-field driving method is employed, the flickering is caused on each line. Thus, even though the flickering is cancelled out between neighboring lines, the flickering does not become imperceptible in actuality, thereby deteriorating visibility significantly. Moreover, with this method, the reduction of the driving frequency is limited, so that the reduction of the electricity consumption is not satisfactory. Further, in the multi-field driving method, where the scanning of one picture screen is carried out in such a manner that every other scanning signal line or every other several scanning signal lines are scanned so that scanning is performed in installment, it is necessary to read a signal corresponding to the scanning signal line, which is currently being driven, after temporal storing of an image in a frame memory. As a result, it is inevitable that the multi-field driving method have a complicated circuit arrangement. Thus, it is a demerit of the multi-field driving method that the multi-field driving method requires a large peripheral circuit, resulting in a high cost.
Furthermore, in the above-mentioned method disclosed in Japanese Unexamined Patent Application, Tokukaihei, No. 6-342148, gradient display cannot be performed, because the ferroelectric liquid crystal basically carries out binary (black and white) display. Moreover, in order to make a liquid crystal panel of the ferroelectric liquid crystal, an advanced panelling technology is required. Therefore, application of this method is difficult and has not been put into practice until today.
As discussed above, none of the conventional driving methods for the matrix-type LCDs have achieved satisfactory and simple reduction of the electricity consumption with good fundamental display qualities, such as the brightness, contrast, response speed, and gradient. Furthermore, the conventional driving methods for the matrix-type LCDs cannot have satisfactory reduction of the electricity consumption and high display qualities. Those problems are not limited to LCDs, but common to any display apparatus of the matrix type.
The invention has an objective to offer a method, of driving a matrix display apparatus, which readily achieves sufficient reduction in electric consumption while satisfying basic display quality requirements including brightness, contrast, responding speed, and gradient, and also to offer a display apparatus to implement the method.
A method of driving a display apparatus in accordance with the invention, in order to achieve the above objective, is a method of driving a display apparatus including a screen which has pixels arranged in a matrix and producing a display by applying a scanning signal to scanning signal lines connected to the pixels and thus selecting a line to scan the screen and also by supplying a data signal to those pixels on the selected line via data signal lines and is characterized in that the method includes the step of providing, after scanning the screen twice or more, an idle period in which all the scanning signal lines are caused to be in a non-scanning state for a period longer than a time taken to scan the screen once.
According to the method, all the scanning signal lines are caused to be in a non-scanning state in the idle period, which reduces the number of times to rewrite the picture, that is, the output time of the data signal. Therefore, the provision of the idle period readily reduces the output time of the data signal, in other words, the electric consumption by a data signal line driver (source driver), or the electric power to charge the pixels, which increases in proportion to the supply frequency of the data signal, in, for example, an active-matrix-drive liquid crystal display.
Further, according to the method, by scanning the screen twice or more, writing can be carried out repeatedly until, for example, the response for display is completed; therefore, the response can be completed in a period shorter than a repetition interval composed of two or more scanning periods and an idle period.
More specifically, when a data signal is supplied to the pixels of the selected line via data signal lines, upon a change in the image to be displayed, a single rewrite of the picture falls short of applying a predetermined voltage to produce desired luminance to the pixel electrodes, and two or more rewrites are required to apply the predetermined voltage.
However, according to the method, by providing an idle period after the screen is scanned twice or more, a sufficient display responding speed is ensured even with the provision of the idle period, and basic display quality requirements are satisfied including brightness, contrast, responding speed, and gradient.
Therefore, by providing an idle period after scanning the screen twice or more, that is, after performing the scan to rewrite one picture twice or more, sufficient reduction in electric consumption can be readily achieved while ensuring a sufficient display responding speed and satisfying basic display quality requirements, such as brightness, contrast, responding speed, and gradient.
Another method of driving a display apparatus in accordance with the invention, in order to achieve the above objective, is a method of driving a display apparatus including a screen which has pixels arranged in a matrix and producing a display by applying a scanning signal to scanning signal lines connected to the pixels and thus selecting a line to scan the screen and also by supplying a data signal to those pixels on the selected line via data signal lines and is characterized in that the method includes the step of providing, when there is no change in an image to be displayed, an idle period in which all the scanning signal lines are caused to be in a non-scanning state for a period longer than a scanning period in which the screen is scanned once after the scanning period and when there has been a change in an image to be displayed, the idle period after the screen is scanned twice or more.
According to the method, by switching the drive of the display apparatus when there is no change in an image to be displayed and when there has been a change in an image to be displayed, optimum response and display quality as well as lower electric consumption, are achieved for every kind of display image including still pictures and dynamic pictures. For example, according to the method, all the scanning signal lines are caused to be in a non-scanning state in the idle period, which reduces the number of times to rewrite the picture, that is, the output time of the data signal. Therefore, the provision of the idle period readily reduces the output time of the data signal, in other words, the electric consumption by a data signal line driver (source driver), or the electric power to charge the pixels, which increases in proportion to the supply frequency of the data signal, in, for example, an active-matrix-drive liquid crystal display apparatus.
In this situation, when there is no change in an image to be displayed, an idle period in which all the scanning signal lines are caused to be in a non-scanning state for a period longer than a scanning period in which the screen is scanned once is provided after the scanning period. Thus, the electric power consumed in the rewriting of the picture can be reduced in the production of still pictures and other motionless displays (displays of non-animated images) and also dynamic pictures which include few motions, while satisfying basic display quality requirements, such as brightness, contrast, responding speed, and gradient.
Meanwhile, when there has been a change in an image to be displayed, by scanning the screen twice or more, writing can be carried out repeatedly until, for example, the response for display is completed; therefore, the response can be completed in a period shorter than a repetition interval composed of two or more scanning periods and an idle period.
As mentioned earlier, when a data signal is supplied to the pixels of the selected line via data signal lines, upon a change in the image to be displayed, a single rewrite of the picture falls short of applying a predetermined voltage to produce desired luminance to the pixel electrodes, and two or more rewrites are required to apply the predetermined voltage.
However, according to the method, by providing an idle period after the screen is scanned twice or more, a sufficient display responding speed is ensured even with the provision of the idle period, and basic display quality requirements are satisfied including brightness, contrast, responding speed, and gradient.
Therefore, the screen is scanned only once in a normal situation, that is, when there is no change in an image to be displayed, and the screen scan is repeated twice or more and only when the display is switched, that is, when there has been a change in an image to be displayed; thus, the number of times to rewrite the picture, that is, the output time of the data signal, can be further reduced and the electric consumption can also be further reduced, while ensuring a sufficient display responding speed and satisfy basic display quality requirements, such as brightness, contrast, responding speed, and gradient.
Another method of driving a display apparatus in accordance with the invention, in order to achieve the above objective, is a method of driving a display apparatus including a screen which has pixels arranged in a matrix and producing a display by applying a scanning signal to scanning signal lines connected to the pixels and thus selecting a line to scan the screen at a predetermined rewrite cycle and also by supplying a data signal to those pixels on the selected line via data signal lines and is characterized in that the method includes the step of scanning the screen at a rewrite cycle longer than the predetermined rewrite cycle when there is no change in an image to be displayed and at the predetermined rewrite cycle only when there has been a change in an image to be displayed.
According to the method, by switching the drive of the display apparatus when there is no change in an image to be displayed and when there has been a change in an image to be displayed, optimum response and display quality as well as lower electric consumption, are achieved for every kind of display image including still pictures and dynamic pictures. For example, according to the method, when there is no change in an image to be displayed, the number of times to rewrite the picture, that is, the output time of the data signal, can be further reduced by setting the rewrite cycle in scanning periods longer than usual, that is, longer than the predetermined rewrite cycle. Thus, the electric consumed in the rewriting of the picture can be reduced in the production of still pictures and other motionless displays (displays of non-animated images) and also dynamic pictures which include few motions, while ensuring basic display quality requirements including brightness, contrast, responding speed, and gradient.
Meanwhile, when there has been a change in an image to be displayed, by scanning the screen at a normal rewrite cycle, that is, the predetermined rewrite cycle, the display better follows changes in the image, and the image changes rapidly.
In this situation, in the foregoing method of driving a display apparatus, preferably, the screen is scanned twice or more at the predetermined rewrite cycle only when there has been a change in an image to be displayed.
A display apparatus in accordance with the invention, in order to achieve the above objective, is a display apparatus including a screen which has pixels arranged in a matrix and producing a display by applying a scanning signal to scanning signal lines connected to the pixels and thus selecting a line to scan the screen and also by supplying a data signal to those pixels on the selected line via data signal lines and is characterized in that the display apparatus includes a control section for controlling drive of the display apparatus, wherein the control section causes all the scanning signal lines to be in a non-scanning state for a period longer than a time taken to scan the screen once after the screen is scanned twice or more.
According to the arrangement, the control section causes all the scanning signal lines to be in a non-scanning state for a period longer than a time taken to scan the screen once after the screen is scanned twice or more, thereby reducing the number of times to rewrite the picture, that is, the output time of the data signal. Therefore, the output time of the data signal, in other words, the electric consumption by a data signal line driver (source driver), or the electric power to charge the pixels, which increases in proportion to the supply frequency of the data signal is readily reduced in, for example, an active-matrix-drive liquid crystal display apparatus.
Further, according to the arrangement, the control section scans the screen twice or more and thereafter causes all the scanning signal lines to be in a non-scanning state for a period longer than a time taken to scan the screen once. Thus, prior to causing all the scanning signal lines to be in a non-scanning state, writing can be carried out repeatedly until, for example, the response for display is completed; therefore, the response can be completed in a period shorter than a repetition interval composed of a period (scanning period) in which the screen is scanned twice or more and a period (idle period) in which all the scanning signal lines are caused to be in a non-scanning state for a period longer than a time taken to scan the screen once.
Therefore, according to the arrangement, a display apparatus can be offered with which sufficient reduction in electric consumption can be readily achieved while ensuring a sufficient display responding speed and satisfying basic display quality requirements, such as brightness, contrast, responding speed, and gradient.
A display apparatus in accordance with the invention, in order to achieve the above objective, is a display apparatus including a screen which has pixels arranged in a matrix and producing a display by applying a scanning signal to scanning signal lines connected to the pixels and thus selecting a line to scan the screen and also by supplying a data signal to those pixels on the selected line via data signal lines and is characterized in that the display apparatus includes a control section for controlling drive of the display apparatus; and a detection section for detecting a change in an image to be displayed, wherein according to a result of the detection by the detection section, the control section causes, when there is no change in an image to be displayed, all the scanning signal lines to be in a non-scanning state for a period longer than a time taken to scan the screen once after the screen is scanned once and, when there has been a change in an image to be displayed, all the scanning signal lines to be in a non-scanning state for a period longer than a time taken to scan the screen once after the screen is scanned twice or more.
According to the arrangement, the display apparatus includes the control section and the detection section, and the control section controls the drive of the display operation, that is, the display apparatus, switchably when there is no change in an image to be displayed and when there has been a change in an image to be displayed, according to a result of the detection by the detection section; therefore, electric power consumed in the rewriting of the picture can be reduced in the production of still pictures and other motionless displays (displays of non-animated images) and dynamic picture which include few motions, while satisfying basic display quality requirements, such as brightness, contrast, responding speed, and gradient.
Specifically, the number of times to rewrite the picture, that is, the output time of the data signal can be reduced by causing all the scanning signal lines to be in a non-scanning state for a period longer than a time taken to scan the screen once. Therefore, by causing all the scanning signal lines to be in a non-scanning state for a period longer than a time taken to scan the screen once, the output time of the data signal, in other words, the electric consumption by a data signal line driver (source driver), or the electric power to charge the pixels, which increases in proportion to the supply frequency of the data signal, can be readily reduced in, for example, an active-matrix-drive liquid crystal display apparatus.
However, when a data signal is supplied to the pixels of the selected line via data signal lines, upon a change in the image to be displayed, a single rewrite of the picture falls short of applying a predetermined voltage to produce desired luminance to the pixel electrodes, and two or more rewrites are required to apply the predetermined voltage:
Accordingly, in the arrangement, when there has been a change in an image to be displayed, by scanning the screen twice or more, writing can be carried out repeatedly until, for example, the response for display is completed; therefore, the response can be completed in a period shorter than a repetition interval composed of a period (scanning period) in which the screen is scanned twice or more and a period (idle period) in which all the scanning signal lines are caused to be in a non-scanning state for a period longer than a time taken to scan the screen once.
Therefore, according to the arrangement, a display apparatus is achieved which further reduces the number of times to rewrite the picture, that is, the output time of the data signal, and the electric consumption while ensuring a sufficient display responding speed and satisfying basic display quality requirements, such as brightness, contrast, responding speed, and gradient.
Another display apparatus in accordance with the invention, in order to achieve the above objective, is a display apparatus including a screen which has pixels arranged in a matrix and producing a display by applying a scanning signal to scanning signal lines connected to the pixels and thus selecting a line to scan the screen at a predetermined rewrite cycle and also by supplying a data signal to those pixels on the selected line via data signal lines and is characterized in that the display apparatus includes a control section for controlling drive of the display apparatus; and a detection section for detecting a change in an image to be displayed, wherein the control section controls application of the scanning signal to the scanning signal lines according to a result of the detection by the detection section so that the screen is scanned at a rewrite cycle longer than a predetermined rewrite cycle when there is no change in an image to be displayed and at the predetermined rewrite cycle only when there has been a change in an image to be displayed.
According to the arrangement, the display apparatus includes the control section and the detection section, and the control section controls the drive of the display operation, that is, the display apparatus, switchably when there is no change in an image to be displayed and when there has been a change in an image to be displayed, according to a result of the detection by the detection section; therefore, electric power consumed on the rewriting of the picture can be reduced in the production of still pictures and other motionless displays (displays of non-animated images) and dynamic picture which include few motions, while satisfying basic display quality requirements, such as brightness, contrast, responding speed, and gradient.
Specifically, the control section controls the application of the scanning signal to the scanning signal lines according to a result of the detection by the detection section so that the screen is scanned at a rewrite cycle longer than a predetermined rewrite cycle when there is no change in an image to be displayed and at the predetermined rewrite cycle only when there has been a change in an image to be displayed. Thereby, the number of times to rewrite the picture, that is, the output time of the data signal can be reduced when there is no change in an image to be displayed. Therefore, the output time of the data signal, in other words, the electric consumption by the data signal line driver (source driver), or the electric power to charge the pixels, which increases in proportion to the supply frequency of the data signal, can be readily reduced in, for example, an active-matrix-drive liquid crystal display apparatus.
Further, when there has been a change in an image to be displayed, by scanning the screen at a predetermined rewrite cycle, the display better follows changes in the image, and the image changes rapidly.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.